The present invention relates in general to substrate manufacturing technologies and in particular to methods and arrangement for the reduction of byproduct deposition in a plasma processing system.
In the processing of a substrate, e.g., a semiconductor wafer or a glass panel such as one used in flat panel display manufacturing, plasma is often employed. As part of the processing of a substrate (chemical vapor deposition, plasma enhanced chemical vapor deposition, physical vapor deposition, etc.) for example, the substrate is divided into a plurality of dies, or rectangular areas, each of which will become an integrated circuit. The substrate is then processed in a series of steps in which materials are selectively removed (etching) and deposited (deposition) in order to form electrical components thereon.
Many plasma processes include some type of plasma bombardment. For example, pure ion etching, often called sputtering, is used to dislodge material from the substrate (e.g., oxide, etc.). Commonly an inert gas, such as Argon, is ionized in a plasma and subsequently accelerate toward a negatively charged substrate. Likewise, reactive ion etch (RIE), also called ion-enhanced etching, combines both chemical and ion processes in order to remove material from the substrate (e.g., photoresist, BARC, TiN, Oxide, etc.). Generally ions in the plasma enhance a chemical process by striking the surface of the substrate, and subsequently breaking the chemical bonds of the atoms on the surface in order to make them more susceptible to reacting with the molecules of the chemical process.
However, a plasma processing system may also produce pollutants. Generally comprised of organic and inorganic byproducts, pollutants are generated by the plasma process from materials in the etchant gases (e.g., carbon, fluorine, hydrogen, nitrogen, oxygen, argon, xenon, silicon, boron, chlorine, etc.), from materials in the substrate (e.g. photoresist, silicon, oxygen, nitrogen, aluminum, titanium, etc.), or from structural materials within the plasma processing chamber itself (e.g., aluminum, quartz, etc.).
Some pollutants are volatile, and may be substantially pumped away by a vacuum system, while other pollutants form non-volatile or low-volatile sputtered species that tend to be deposited on interior surfaces and plasma chamber walls that tend to be difficult to efficiently evacuate from the plasma chamber. The resulting pollutant deposits may eventually flake and hence increase susceptibility of substrate defects, reduce the mean time between cleaning (MTBC), reduce yield, etc. For example, depending on the plasma process, conductive film deposits may form on plasma chamber interior surfaces which may impact the FW coupling of the plasma source and bias. In addition, byproduct deposits may contribute to plasma density drift.
Non-volatile and low-volatile byproducts include direct line-of-sight deposition of sputtered material, direct ion enhance etch byproduct deposition, volatile byproduct condensation, high sticking coefficient plasma dissociated byproducts, ion assisted deposition of plasma species, etc. Examples include high-k dielectrics (HfOx, HfSixOy, etc) byproducts, metal electrode (Pt, Ir, IrOx, etc.) byproducts, memory material byproducts (PtMn, NiFe, CoFe, FeW, etc), interconnect byproducts (Cu, Ru, CoWP, Ta, etc.).
In general, the emission profile for the sputtered atoms is generally characterized by a cosine distribution. This means that the emission rate at some angle other than normal (perpendicular) is equal to the normal incidence emission rate times the cosine of the angle from the normal. This is usually drawn as a circle touching the impact point, in which the circle is the envelope of the magnitudes of the emission at other angles. Generally, since sputtered atoms tend to be neutral, it is not possible to redirect their trajectories in flight, and hence the sputtered atoms tend to travel in straight lines.
The degree of deposit adhesion to surfaces within the chamber, and hence the subsequent degree of potential contamination, is usually dependent on the specific plasma processing recipe (e.g., chemistry, power, and temperature) and the initial surface condition of chamber process kits. Since substantially removing deposits may be time consuming, a plasma processing system chamber is generally substantially cleaned only when particle contamination levels reach unacceptable levels, when the plasma processing system must be opened to replace a consumable structure (e.g., edge ring, etc.), or as part of scheduled preventive maintenance (PM).
Referring now to FIG. 1, a simplified diagram of an inductively coupled plasma processing system, such as a Lam Research Transformer Coupled Plasma Processing System™, is shown. In a common configuration, the plasma chamber is comprised of a bottom piece 150 located in the lower chamber, and a detachable top piece 152 located in the upper chamber. Generally, an appropriate set of gases is flowed into chamber 102 from gas distribution system 122 and through dielectric coupling window 104. These plasma processing gases may be subsequently ionized at injector 108 to form a plasma 110 in a plasma generating region, in order to process (e.g., etch or deposition) exposed areas of substrate 114, such as a semiconductor substrate or a glass pane, positioned with edge ring 115 on an electrostatic chuck 116.
A first RF generator 134 generates the plasma as well as controls the plasma density, while a second RF generator 138 generates bias RF, commonly used to control the DC bias and the ion bombardment energy. Further coupled to source RF generator 134 is matching network 136a, and to bias RF generator 138 is matching network 136b, that attempt to match the impedances of the RF power sources to that of plasma 110. Furthermore, pump 111 is commonly used to evacuate the ambient atmosphere from plasma chamber 102 in order to achieve the required pressure to sustain plasma 110.
While these are severe issues to tackle requiring complicated high temperature chamber designs, special materials etc, there is no commonality to the behavior of these different materials. For example, if plasma process conditions allow it, a clean or a self-cleaning plasma recipe can be developed, or the chamber surfaces can be designed with materials that have a reduced sticking coefficient to the problem byproduct, or if the byproducts are sufficiently adhered or “stuck” to the chamber surfaces, the plasma process can be run until flaking becomes problematic. However, since these solutions are very process sensitive, the possibility of a single robust reactor design and process approach which can handle most of these materials and potential chemistries is problematic.
In view of the foregoing, there are desired methods and arrangement for the reduction of byproduct deposition in a plasma processing system.